1. Field of the Invention
The present invention relates to liquid level indicator controllers and more particularly to a purge bubbler liquid level control system having a mercury manometer.
2. Description of the Prior Art
Many systems are in use for maintaining a predetermined level in a standpipe, tank, or water supply system. Many of these utilize mechanical floats in the liquid which may operate external electrical switches, diaphragm-type pressure switches set to operate at specific pressure levels, and other types of liquid level sensors for controlling the appropriate pumps. Where levels are to be determined at remote locations, it is common to use a purge bubbler system in which an air compressor places pressure on a line to the liquid-containing vessel such that air forced through the line will bubble out through the liquid. The resultant hydrostatic back pressure in the line at the remote location is then suitably sensed and used to control the pumps or other means for control of the liquid level. As the liquid level changes it, of course, changes the sensed pressure in the bubbler line. The flow of air through the bubbler line, in addition to balancing the liquid head pressure, maintains a constant purging action to prevent clogging of the sensing line.
The present invention is a purge bubbler system type in which a mercury manometer having electrical contacts for sensing specific liquid levels is used. A typical prior art system of this type has been described in Bulletin No. 13D2425, published by Fischer and Porter Company. The Fischer and Porter system uses a mercury manometer having a mercury column with contacts embedded in the walls of the column, and a complicated and expensive electrical terminal arrangement for connecting to these contacts. The manometer requires a separate mercury reservoir and associated tubing and fittings to connect to the column. The manometer also uses an overflow reservoir for preventing loss of the mercury from blowouts, surges or accidental excess pressure on the manometer. This technique while saving the mercury, requires installation of mercury by the user since the manometer cannot be shipped in the filled condition. The manometer in the present invention provides a low cost, simplified construction with protection from overflow and represents a significant improvement over the known prior art.